Cyclopentadiene nickel derivative

Whether the nickel complexes formed from diorgano ditellurium derivatives and cyclopentadienyl(cyclopentadiene)nickel tetrafluoroborate in diethyl ether at 20° contain an intact diorgano ditellurium ligand or two tellurolato ligands is not known4. 

Bis-(l,5-cyclopentadiene)nickel(0) Ethylene derivs. from l,3-dioxolane-2-thiones s. 19,962 suppl. 28... 

Raney-nickel was found to be selective in the hydrogenation of cyclopentadiene and cyclohexadiene and of their methyl and ethyl derivatives at 0-40 °C and 2-5 bar pressure137,138. The skeletal nickel proved to be selective in the semihydrogenation of conjugated polyenic compounds (equation 52)139. 

FIGURE 1. Possible orientations of phosphine derivatives of cyclopentadiene iron and nickel complexes. The Fe(II) and Ni(II) ions lie behind the circle of Newman s rendition of the complexes... 

The dimeric azaphospholines derived from (/ )-myrtenal and (J )-l-phenylethylamine are also active ligands in the nickel catalyzed hydrovinylation of cyclopentadiene with ethylene to give exclusively 3-vinylcyclopentene (7) with 100% chemo- and regioselectivity and up to 76% ee5 (according to recent reports even higher inductions are obtainable53). No isomerization and dimerization of the products is observed. Previously, with other catalytic systems the same... 

The chiral iron(III) Lewis acid 3, derived from an oxazoline ligand, catalyzes Diels-Alder reactions of A -acryloyl-l,3-oxazolidinone (1) and cyclopentadiene (2) with good enantiomeric excess30. Nickel complexes of chiral phosphanes also catalyze Diels-Alder reactions albeit with low enantiomeric excess, not exceeding 15% cc31. Much better results are achieved for cobalt complexes with chiral phosphanes in the presence of a Lewis acid31,32. 

In the last decade, several excellent results were also published in the area of enantioselective nickel-catalysed Diels-Alder cycloadditions. Among them, the reactions of cyclopentadiene with 3-alkenoyloxazolidin-2-ones induced by (i )-BINIM-2QN provided cycloadducts in up to >99% yield, >98% de, and 96% ee. Another excellent result was achieved by using a chiral iV,iV -oxide-derived nickel catalyst in Diels-Alder cycloadditions of 3-vinylindoles with methyleneindolinones for the construction of chiral spiro[carbazole-oxindoles] in up to 97% yield, >98% de, and 98% ee. Moreover, the use of the chiral DBFOX-Ph ligand has allowed an inverse-electron-demand Diels-Alder reaction of a range of Af-sulfonyl-l-azadienes with vinyl ethers to be achieved, providing highly functionalised piperidines in up to 75% yield, 96% de, and 92% ee. 

The third type of single-site catalyst is best described as a nonmetallocene type of catalyst system, where a ligand system is used that is not based on a cyclopentadiene derivative. This third type of single-site catalyst may utilize a very wide variety of ligands and an early or late transition metal (i.e., iron, cobalt or nickel) maybe utilized as the active center [9-13]. 

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